P0129Generic code

P0129 Code: Barometric Pressure Too Low

The P0129 code means the measured atmospheric pressure is lower than it can physically be. It is usually caused by a defective BARO or MAP sensor or its circuit, not by altitude.

Severity
Medium
Can I keep driving?
Yes, but with caution
Estimated cost
$40 to $300
Difficulty
Medium
System
Air and Fuel
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0129 code means

The computer needs barometric pressure to correct the mixture for altitude. Some vehicles have their own BARO sensor, others build it into the computer, and many use the MAP sensor with the engine off.

If the measured pressure is below what is physically possible even at high altitude (for example, less than 50 to 60 kPa, or about 7 to 9 psi), the computer stores the P0129 code. Test the MAP sensor as part of the diagnosis.

P0129 code symptoms

  • Check engine light on.
  • Wrong mixture: jerking or high fuel use.
  • On turbo engines, incorrect boost pressure control.

Likely causes of the P0129 code

  1. Defective BARO or MAP sensor.
  2. Vacuum hose or sensor port clogged.
  3. Low 5 V reference shared with other sensors.
  4. Connector with corrosion.
  5. BARO sensor inside the computer on some vehicles, which is uncommon.

How to diagnose the P0129 code step by step

  1. With the engine off, compare the BARO reading with the real pressure. It should be about 100 kPa (14.5 psi) at sea level and about 75 kPa (10.9 psi) at 2,500 m (about 8,200 feet).
  2. Compare BARO and MAP with the key on. They should agree.
  3. Check the sensor port for clogs.
  4. Check 5 V and ground.
  5. Look for manufacturer bulletins.

How to fix the P0129 code

  • Clean or repair the sensor port.
  • Repair the 5 V reference if it is low.
  • Replace the sensor if it reads wrong.
  • Clear the codes and verify.

Technical reference data

  • Barometric pressure: 101 kPa (14.7 psi) at sea level, about 90 kPa (13.1 psi) at 1,000 m (3,300 feet), about 80 kPa (11.6 psi) at 2,000 m (6,600 feet).
  • Values are approximate.

Brand-specific notes

With a P0129 code, it helps to know where the BARO sensor lives on your vehicle, because the location changes by manufacturer.

P0129 on Chrysler

On many Chrysler vehicles the BARO sensor is inside the computer.

P0129 on Nissan

On many Nissan vehicles the BARO sensor is inside the computer.

P0129 on Volkswagen

On Volkswagen and other diesels, the BARO sensor is usually built into the boost pressure sensor.

Frequently asked questions about P0129

Can altitude cause the P0129 code?
Not under normal conditions. The code limit is below the pressure of any inhabited city.
Can I drive with a P0129 code?
Yes, with caution. The mixture may not be correct.
Which sensor measures barometric pressure?
It depends on the vehicle: a BARO sensor, the MAP sensor with the engine off, or a sensor inside the computer.
How much does it cost to fix P0129?
Roughly $40 to $300.
What does the P0129 code mean?
It is a generic OBD2 code that means the barometric pressure reading is lower than is physically possible. It points to a defective sensor or its circuit.
What is the most common cause of P0129?
A defective BARO or MAP sensor, or a problem in its circuit such as a clogged port or a low 5 V reference.

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